This invention relates to a parachute extraction system for airdropping heavy equipment or cargo from an aircraft and, more particularly, to an apparatus and method for severing the parachute extraction line in the event of an airdrop malfunction.
Under normal airdrop conditions, the drag force created by the inflation of an extraction parachute deployed behind the aircraft is utilized to extract cargo therefrom and deploy a recovery parachute from which the extracted load is suspended and lowered to the earth's surface. Alternately, the extraction parachute alone can be utilized to both extract the load from the aircraft as well as lower the load to the earth's surface.
The cargo to be extracted from a cargo aircraft is fixedly secured to a pallet or platform adapted to be moved longitudinally on a roller conveyor mounted along the floor of a cargo compartment. Generally, cargo aircraft employ two separate and distinct, laterally spaced releasable locking mechanisms for restraining the pallet and its associated load in the aircraft. The locking mechanism (left-hand locks) located on the left side of the cargo compartment are called the logistics locks and are engaged or disengaged by the loadmaster. These locks are disengaged prior to reaching the airdrop point. The right-hand locks, also called the Air Drop System (ADS) locks, are operative in the same manner as the left-hand locks. However, the right-hand locks can be set to release or disengage automatically upon the application of a predetermined force, such as that generated by a fully inflated extraction parachute. This prevents the extraction of the load if the extraction parachute does not deploy properly or does not fully inflate.
In operation, the left-hand locks are released a few minutes prior to the time of the airdrop. The loadmaster visually confirms that the left-hand locks are disengaged. The rear door of the aircraft is then opened and, at the proper time, the extraction parachute is discharged through the aircraft's aft open end for deployment. When the extraction parachute is fully inflated, the drag force supplied by the extraction parachute to the load overcomes the release force set in the right-hand locks. The locks are thus disengaged and the extraction parachute becomes effective to withdraw, via the extraction line, the cargo-laden pallet as well as the recovery parachute from the aircraft. As the pallet leaves the aircraft, a force transfer coupling transfers the extraction force from the cargo-laden pallet to the bags holding the recovery parachutes. The bags and recovery parachutes are pulled away from the now free falling cargo-laden pallet until the suspension slings attaching the recovery parachutes to the cargo-laden pallet are fully extended. At this point, the extraction parachute pulls the bag from the recovery parachutes, the recovery parachutes inflate, and the cargo-laden pallet is slowly lowered to the ground.
A serious problem with the above procedure resides in a cargo airdrop malfunction wherein the load is not extracted even though the extraction parachute has deployed properly but for some reason the load fails to exit the aircraft, or because the extraction parachute does not properly deploy or inflate. In either case, the loadmaster must first try to re-engage the left-hand locks. However, once the left-hand locks have been released and an extraction force has been applied, it is often impossible to re-engage the locks. Failing to re-engage the left-hand locks, the loadmaster must chain the pallet to the floor to make it safe to move aft of the load to manually cut the extraction line with a knife. Should the load free itself with the malfunctioning locks released, the load could then be extracted from the aircraft, taking the loadmaster with it. An even worse condition occurs when the drag force of the extraction parachute exceeds the thrust capabilities of the aircraft's engines. In this event, should the load fail to exit the aircraft due to any number of reasons, the extraction line must be cut quickly or the aircraft will lose airspeed and possibly crash.